Silent Partner by Jonathan Kellerman

At a party for a controversial Los Angeles sex therapist, Alex encounters a face from his own past--Sharon Ransom, an exquisite, alluring lover who left him abruptly more than a decade earlier. Sharon now hints that he desperately needs help, but Alex evades her. The next day she is dead, an apparent suicide. Driven by guilt and sadness, Alex plunges into the maze of Sharon's life--a journey that will take him through the pleasure palaces of California's ultra-rich, into the dark closets of a family's disturbing past, and finally into the alleyways of the mind, where childhood terrors still hold sway.